01 - Preheat oven to 350°F. Place unbaked pie crust in a 9-inch pie pan and trim or crimp edges as preferred.
02 - Combine whole milk and heavy cream in a medium saucepan. Warm gently over medium heat until steaming but not boiling. Remove from heat.
03 - In a mixing bowl, whisk together eggs, granulated sugar, cornstarch, vanilla extract, ground cinnamon, and salt until completely smooth.
04 - Slowly pour the hot milk mixture into the egg mixture in a steady stream while whisking constantly to combine and gently heat the eggs.
05 - Strain custard through a fine-mesh sieve into a clean bowl to remove any lumps, then pour into the prepared pie crust.
06 - Transfer pie to the oven and bake for 45 to 50 minutes, until custard is set but center jiggles slightly. Shield crust edges with foil if browning too quickly.
07 - Remove from oven and place pie on a wire rack. Cool to room temperature; the custard will finish setting as it cools.
08 - Sprinkle surface with ground cinnamon and optionally dust with powdered sugar before serving.
09 - Refrigerate pie at least 2 hours before slicing for clean, neat portions.